Sterilization of instruments and equipment used in medical and surgical procedures is important to prevent post-surgical infections in patients. Hospitals and medical facilities utilize a variety of cleaning and sterilization techniques and methods to re-process soiled or previously used surgical instruments. A hospital or medical center typically includes a sterile processing department that handles the cleaning and sterilization of medical instruments of the facility.
The sterile processing department commonly has several sections including a cleaning section, a sterilization section and a sterile storage section. Surgical equipment used during medical procedures return from the operating room to the cleaning section. In the cleaning section, the surgical instruments are cleaned of any visible liquid or solid medical waste and processed through a manual or an automated washing process. The automated washer uses high pressure streams of water and detergent to remove debris and residue from instrument surfaces. The washer exposes surgical instruments to high temperature water and sometimes damaging chemicals for a period of time. Some surgical instruments are not amenable to processing through the automated washer and are required to be manually washed.
After washing, the surgical instruments undergo a functional equipment inspection to check for broken parts or defects in the surgical equipment. Defective parts are repaired or replaced. Next, the individual surgical instruments are prepared for sterilization by placement of the surgical instruments in containers. Some surgical instruments are required to have a certain geometrical orientation during the sterilization process so that sterilant may effectively enter, contact and leave the surgical equipment during processing. The instruments can be grouped together by procedure to form a surgical tool set.
To preserve the sterility of the surgical instruments during handling and storage after sterilization, surgical instruments are typically placed into various container systems that form a sterile barrier around the instruments. Given that this barrier is intended to prevent ambient microbial organisms from adhering to the sterilized instruments these barriers are sometimes referred to as microbial barriers or SBSs (sterile barrier systems). One popular container system in use today is one that is constructed with two types of materials, one material being a “rigid” impermeable material and the other material that is a microbial filter. The microbial filter is constructed to allow the sterilizing agent, typically a vapor or gas, to penetrate during sterilization but prevents microorganisms such as mycobacterium, vegetative bacteria, viruses, fungi, and bacterial spores from entering the container. Another container system is formed by using a perforated “rigid” material such as aluminum or stainless steel and the entire perforated container is wrapped with a microbial filter like material. The perforated “rigid” material provides structure to transport, handle and stack the containers of surgical instruments, but by itself does not prevent micro-organisms from entering the container. The sterile barrier material protects the surgical instruments from contamination during post sterilization handling and storage. The outer sterile wrap can be a spun polypropylene wrap and is permeable to sterilizing fluids or gases while forming a microbial barrier. When a container system is not used, individual surgical instruments can be packed in a flexible envelope material such as Tyvek typically constructed of a semi-permeable Tyvek on one side to allow the sterilizing agent to ingress and egress, and a non-permeable Mylar on the other side that allows the contents to be viewed
To visually verify that containers of surgical instruments have been exposed to sterilizing agents, chemical indicators may be added to the inside and/or the outside of the sterile barrier system prior to undergoing the sterilization process. Chemical indicators are specifically designed for the type of sterilizing agent, gas or vapor used. The Class I Chemical Indicator is a chemical indicator system recognized by the FDA and JCAHO for use in hospitals in the United States. European regulatory agencies currently recognize proof of exposure chemical indicators, which provide parametric release, as well as Class I chemical indicators. A Class I chemical indicator provides a visual indication that it has been exposed to a sterilization agent, but does not indicate the level of exposure or amount of time of exposure. External chemical indicators are typically used so the hospital sterile processing department personnel can determine where the individual containers of equipment are in the workflow within the department and the internal chemical indicators are used to indicate to the hospital personnel setting up for a surgical procedure that the equipment inside of the sterile barrier has been exposed to a sterilization agent. If the external chemical indicator does not indicate exposure to the sterilization agent within the Sterile Processing Department, the surgical tool set must be processed to insure sterility. If the internal chemical indicator does not indicate exposure to the sterilization agent when the container is opened, the container and equipment must be returned to the Sterile Processing Department for reprocessing, typically beginning with the cleaning process. Determining that a container of surgical equipment has not been exposed to a sterilizing agent, while preparing for a surgical procedure is disruptive to the efficiency of the operating room and requires that another set of surgical equipment be located and properly set ultimately causing schedule delays and/or other adverse disruptions. Various types of chemical indicators have been developed including tapes, paper strips and catalytically activated systems. Tapes, labels, and paper strips are printed with an ink that changes color when exposed to a specific sterilization agent or chemical. Integrating or wicking paper is made with an ink or chemical at one end that melts and wicks along the paper over time under the desired process values. A color bar reaches an acceptable area if the process values are met. The chemical indicators are different for the various types of sterilization modalities, and thus the chemical indicator visual changes are not the same across sterilization methods. Sometimes the color change indicating exposure to one modality, e.g. steam autoclave, is opposite the color change for a different sterilizing modality, e.g. hydrogen peroxide sterilization. This causes confusion for the health care workers when reading and interpreting the various chemical indicator color changes.
Once the surgical instruments are fully packed and ready for sterilization, the surgical tool sets are processed through a sterilization process to destroy microorganisms. Various sterilization methods and agents have been used to sterilize surgical instruments.
Saturated Steam heat is one sterilant that is used to destroy microorganisms. Pressures higher than atmospheric pressure are necessary to increase the temperature of the steam for destruction of microorganisms that pose a greater challenge to kill. The saturated steam at a required temperature and time must penetrate and reach every surface of the items to be sterilized. A sterilization chamber contains the articles to be sterilized. When steam initially enters the sterilizer chamber under pressure, it condenses upon contact with cold items. This condensation liberates heat, simultaneously heating and wetting items in the load. The entire load must be exposed to moist heat for a minimum time and at a minimum defined temperature in order to affect sterilization. For example, one type of surgical tool set may require 34 minutes at 270 degrees Fahrenheit to destroy the micro-organisms and another 20 minutes of evacuation to dry the instruments within the sterile barrier so that condensation does not accumulate within the sterile barrier. A minimum temperature-time and steam concentration relationship is required to be maintained throughout all portions within the sterile barrier and across the sterilizer chamber load to complete sterilization. The time, temperature and steam concentration to destroy micro-organisms depends upon many factors. For example the size, surface area, thermal mass, orientations and depths of internal cavities of the contents of the load within the sterile barrier as well as the steam penetration properties of the sterile barrier used can affect the reliability to destroy micro-organisms. After the steam cycle has been completed, the water condensate must be evaporated to dry contents of the load to maintain sterility. A vacuum can be drawn on the chamber to assist in the evaporation of any remaining water. The normative reference commonly used to determine appropriate sterilization exposure times are listed in Table 5 which is taken directly from ANSI/AAMI ST79: 2010/A2: 2011 “Comprehensive Guide to Steam Sterilization and Sterility Assurance in Health Care Facilities, Amendment 2”.
TABLE 5Minimum cycle times for dynamic-air-removal steam sterilization cyclesExposure timeExposure timeItemat 132° C. (270° F.)at 135° C. (275° F.)Drying timesWrapped instruments4 minutes20 to 30 minutes3 minutes16minutesTextile packs4 minutes 5 to 20 minutes3 minutes3 minutesWrapped utensils4 minutes20 minutes3 minutes16 minutesUnwrapped nonporous3 minutes3 minutesNAitems (e.g., instruments)unwrapped nonporous4 minutes3 minutesNAand porous item in mixedloadNOTE-This table represents the variation in sterilizer manufacturers’ recommendations for exposure at different temperatures. For a specific sterilizer,consult only that manufacturers recommendations.
Some surgical equipment such as gastroscopes and endoscopes are sensitive to the steam and high temperatures required by steam sterilization. Hydrogen peroxide vapor is another agent used to sterilize surgical instruments. Hydrogen peroxide is vaporized externally from the sterilization chamber in a defined reaction chamber. The vaporized hydrogen peroxide is introduced into the sterilization chamber, at which point it contacts the sterile barrier and passes through the barrier to contact the contents of the container to be sterilized. The hydrogen peroxide vapor is introduced into a sterilization chamber containing the articles to be sterilized. Hydrogen peroxide sterilizers today typically operate at much lower temperatures than steam sterilizers with maximum temperatures being around 122 degrees Fahrenheit for a hydrogen peroxide sterilizer. A minimum hydrogen peroxide concentration, pressure changing “pulse cycle”, and temperature relationships over time are required to be maintained throughout all portions of the load to complete sterilization. After the hydrogen peroxide vapor cycle has been completed, the chamber is purged of residual and condensed hydrogen peroxide. RF energy may be used to energize the residual hydrogen peroxide vapor during this aeration phase creating a plasma that facilitates the aeration process. Some older plasma systems utilized RF energy during the sterilant exposure phase with the expectation that the plasma phase would be more effective at killing micro-organisms than the vapor phase. Residual hydrogen peroxide is required to be removed from the surgical instruments and packaging prior to use in order to prevent burns and injury to healthcare workers and patients.
Other liquid and gaseous agents can also be used to sterilize surgical instruments such as ethylene oxide gas, formaldehyde gas and ozone gas. These sterilizing agents use “low temperature” sterilization conditions as do the Hydrogen Peroxide sterilizers described above allowing their use on sensitive medical equipment as an alternate to potentially damaging high temperature steam sterilization. Unfortunately, these gases are somewhat higher in toxicity and/or are difficult to control during the sterilization process so they do not enjoy wide-spread use throughout hospital systems.
Regulations within the medical device industry require the Original Equipment Manufacturer (OEM) to provide instructions to the Hospitals and Health care providers on proper use and maintenance of reusable medical equipment. The OEM can be the designer, manufacturer or distributor of reusable medical equipment. Within the category of reusable medical equipment, certain equipment and instruments can become contaminated by biological material from the patient like bodily fluids, mucus and tissue during use so that it must be cleaned and/or sterilized before being used again. Certain reusable medical equipment such as Colonoscopes cannot be sterilized using the equipment in a hospital central processing department. Based on the risks versus benefits analysis sterilization can be replaced by high level disinfection for these devices. The generally accepted definition of a sterilization process is, “the reduction of 10^6 organisms down to zero”, and high level disinfection process is, “the reduction of 10^3 organisms down to zero”. Sterilization is defined as the Sterility Assurance Level (SAL) which utilizes the, “overkill method”, to show a 12 log reduction of the most challenging organism to the method of sterilization being employed. A 12 log reduction means that there is a one in one million probability of a single viable organism surviving the sterilization process. Disinfection is defined in three categories; High Level Disinfection (HLD): Many or all pathogenic microorganisms with the exception of bacterial spores, Intermediate Level Disinfection (ILD): May be cidal for mycobacterium, vegetative bacteria, most viruses, and most fungi; but does not necessarily kill bacterial spores, and Low Level Disinfection (LLD): Kill most vegetative bacteria, some fungi, and some viruses. The OEM is responsible to provide proper cleaning and sterilization (or disinfection) instructions to the Health Care users. The OEM is not allowed to randomly select cleaning and sterilization techniques prior to selling new reusable medical equipment, they are required to validate the cleaning and sterilization processes. For steam sterilization validations OEMs can use the American National Standard ANSI/AAMI ST79 in the United States and ISO 17665-1 in other countries. These mentioned standards are incorporated by reference to this patent application. These standards include sterilization (or disinfection) validation testing protocols for the OEMs regarding the cleaning and sterilization methods so that Health Care facilities do not have to individually validate these methods using their sterilization equipment for each medical device they purchase. Even though these standards are accepted throughout the medical device industry by the Healthcare Regulatory agencies and the Healthcare providers, there is potential for human error, uncontrollable variability and sterilizing system equipment problems that enter into the Healthcare delivery system which may cause inconsistencies in the sterilization or disinfection results for reusable medical equipment. Examples: the OEM validates a new set of equipment per the governing standards. The governing standards require that organism X be used to inoculate the new set of equipment for a given sterilization agent. The OEM follows the governing protocols and validates the new equipment to a 10E-6 Sterility Assurance Level (SAL) using these nominal steam process values in a small chamber steam autoclave able to hold only one set of equipment (e.g. 14″×14″×24″ chamber). The OEMs instructions resulting from the SAL validation could be as follows: Wrapped using 500 grade wrap, Dynamic air removal (pre-vac)cycle, Sterilization temp 132° Celcius, Exposure time 4 minutes, Dry time 30 minutes. The hospital sets up the sterile barrier system and follows all instructions, but instead of a single container autoclave, they have a large steam autoclave where the chamber can hold 40 sterile barrier system containers and a wheeled shelving rack where they roll the loaded rack into the autoclave. Uncontrolled variable: The OEM validated their equipment in an ambient temperature of 25° C. (pre-sterilized equipment started at 25° C.) and the hospital stores their pre-sterilized equipment in a conditioned environment at 20° C. Thermodynamically, the lower starting temperature and a significantly larger total chamber load at the hospital reduces the actual exposure steam/temperature duration below the validated level for proper organism destruction. Human error: the Hospital followed all instructions properly, but a heavy medical instrument that did not have a container was included inside the sterile barrier system. This caused a reduction of the temperature build up of all equipment inside the sterile barrier system. Sterilization equipment problem example: a power spike advances the sterilizer by 1 minute thus shortening the actual exposure duration by that amount. Similar examples can be established for other sterilization processes such as Hydrogen peroxide sterilization processes and methods. Another factor that can cause problems with the sterilization of medical devices is where a mixed load of equipment is sterilized together in a single process. The mixed load in this example is medical equipment that has the same sterilization time duration, but different dry times across the various containers which are sterilized together. If this occurs, there could be some residual moisture retained in the equipment that requires a longer drying time. This residual moisture can wick out. This wicking out results in a water stain forming on the SBS wrap used on a perforated container, but the water stain is not discovered until the operating room personnel are preparing the equipment for the next surgical procedure. Once the operating room personnel notice the water stain during set-up, they have to return all of the equipment for reprocessing to the sterile processing department. The SBS materials are not designed to maintain their anti-microbial properties if they become wet. Since it is not known when or how it became wet, the entire group of equipment becomes suspect due to the water stain and thus must be reprocessed. These are some examples of problems that desire a better system and solution so that healthcare delivery is efficient and safe.
Further, the current practice is to, as part of the process of sterilizing a surgical instrument, perform a test to verify that the sterilizer in which the instrument is sterilized is properly functioning. This test is performed with a biological indicator. A biological indicator includes known number and type of microorganisms that have an appreciable resistance to the mode of sterilization being practiced.
The biological indicator is placed in a tray or container and is processed through a specific sterilization process. The biological indicator can be placed within a sterile barrier and wrap prior to processing such that its exposure to the sterilant is similar to a surgical tool set. Many biological indicators used today are self contained. The self contained biological indicators have a housing sealed to a microbial barrier material that allows a path for the sterilizing agent to penetrate and reach the biological agent, but not allow other micro-organisms to enter. These biological indicators do not require a container or wrap during use.
Therefore, there are typically different biological indicators for each sterilization process modality used in a sterile processing department. This requires the sterile processing department to be trained to properly execute the biological indicator tests for every sterilizer and sterilizing modality within the department. For example if a hospital has both autoclave steam and hydrogen peroxide equipment, the sterile processing department has to purchase and maintain both types of biological indicators and be trained to properly process the biological indicators. Also, the different manufacturers of hydrogen peroxide equipment typically each require a specific biological indicator be used in this test. So if a sterile processing department has two hydrogen peroxide systems, each made by a different manufacturer, the sterile processing department needs to become proficient at operating two biological indicator tests, one for each system. Bacterial spores have been used as biological indicators. The biological indicator is sealed or enclosed in a protective package. After exposure to the sterilization process, the biological indicator is placed in a growth medium and cultivated for a period of time, after which they are read by department personnel. For example, steam autoclave biological indicators use Geobacillus stearothermophilus at a 106 population and are incubated for a minimum of 24 hours in a growth medium. For Hydrogen Peroxide sterilization agents, a Geobacillus stearothermophilus at a 106 population is used and incubated in a growth medium at a specific temperature for 24 hours. Subsequent growth of the biological agent indicates a failure of the sterilization process and subsequent no growth of the biological agent microorganisms under suitable conditions indicates the proper operation of the sterilization process for that particular cycle. Because the biological agent used in biological indicators are more resistant to their specific sterilization agents than common microorganisms potentially found on surgical instruments, the demonstration that the biological indicator has been inactivated provides assurance that other microorganisms, including potential pathogens in the load, have also been destroyed.
For Hydrogen peroxide sterilizers, a typical sterile processing department runs a biological indicator test every 24 hours as a check on the proper operation of the equipment. The biological indicator test is typically run by itself or with the first lot of medical equipment processed through the sterilizer machine for the day. A biological indicator test can take up to 24 hours to complete. Consequently, subsequent loads of surgical instruments and tools are quarantined for the time period required to complete the biological indicator test so as to verify that the sterilizer is properly functioning.
Many sterilization processes take less than an hour to perform. However, owing to the need to verify that the sterilizer is properly functioning, an instrument can be quarantined for up to the additional 24 hours required to obtain the results of the biological indicator test. This means that at a hospital, at any given moment in time, a significant number of the hospital's surgical instruments may be in quarantine. This requires the hospital to have a large inventory of surgical instruments so that, at any given instant, a sufficient number of instruments are sterilized and ready for use. Requiring the hospital to maintain this large inventory of instruments can add to the cost of maintaining the hospital.
If the biological indicator test fails, all of the lots of surgical equipment processed in the sterilizer machine, since the last passed biological indicator test, are potentially non-sterile. This equipment is then reprocessed again through the cleaning and sterilization process.
If first biological indicator test indicates the sterilizer is operating properly, it is assumed that the sterilizer has sterilized the instruments placed in the sterilizer up until the execution of the next biological indicator test. This assumption is made even though there is a possibility that between the two consecutive tests, the sterilizer may start to malfunction. The fact that the sterilizer may have started malfunctioning is not known until the results of the second biological indicator tests are read. In the interim, however, the equipment sterilized between the first and second tests may have been released from quarantine and used in a procedure. This means the equipment used on a patient may be a piece of equipment that was not properly sterilized.
Further, having to execute a biological indicator test requires resources include the time of hospital personnel.
The current processes for determining the proper operation of the various sterilizing equipment's sterilization processes and the use of microbial barriers for subsequent storage have many problems that add time and expense to the entire sterilization process. The use of microbial barriers and wraps to encase surgical instruments adds expense in the purchase of the materials and time for department personnel to wrap and create the sterile barrier containing the surgical instruments. The use of microbial barriers also increases the difficulty of the sterilant to enter the wrapped package and complete sterilization, particularly for low vapor pressure sterilants such as hydrogen peroxide vapor. Variations in sterile barrier materials and how they are applied will introduce variation in the sterilant concentration within the wrapped package. Variations in the mass, materials of construction, and surface area of the instrument load can also introduce variation in the sterilant concentration within the wrapped package.
The use of chemical indicators adds expense in the purchase of the chemical indicators and the time for department personnel to place and read the chemical indictors. The use of biological indicators adds expense in the purchase of the biological indicators and the time for department personnel to place, incubate and subsequently read the results of the biological indictor.
If either of the chemical or biological indicator tests fail, all of the unused lots of surgical equipment processed in the sterilizer machine, since the last acceptable test, must be reprocessed again through the cleaning and sterilization process, adding time, expense and increasing the inventory of surgical instruments required. As discussed above, there is a possibility that instruments that may not have been sterilized were used on patients. If this event occurs appropriate action may need to be taken. In addition, if the sterilizer has an equipment or process problem during one biological incubation period, this problem may not be detectable until the reading at the end of the subsequent biological indicator (BI) incubation period (by reading a failed biological indicator in the subsequent test). This allows the possibility of releasing medical equipment from quarantine from the time the problem occurs (during the first incubation period) until the time of the failed BI test.
Another problem with the current processes for determining the validity of a sterilization process is that many of the steps in the process depend upon human action and judgment and as such are prone to human error. Human error can occur by incorrect orientation and placement of surgical instruments in racks and containers. Human error can occur by placing items so that they block the flow of sterilant into the container and adversely affect sterilization efficacy of the items therein. Human error can occur by placing too many instruments within the container adversely affecting sterilization efficacy. Human error can occur by stacking containers on top of one another so that the sterilant is not able to flow freely into all of them. Human error can occur by incorrectly operating the sterilization machine. Human error can occur by incorrect placement and reading of chemical indicators. Human error can occur by incorrect placement, incubation, and reading of biological indicators.